A Mysterious Nest in the Bluebird Box.

I'd just about given up on any bird using the box-on-a-post I put up last fall (a box intended for Eastern Bluebirds.) As recently as a week ago no signs of activity were observed at or in the box. Inspired by the success of a colleague who immediately drew in bluebirds at a box she just put up, I checked the thing today. To my astonishment, some bird had loaded the biodegradable cup that came with the box. It sure didn't look like a bluebird nest style: far too messy. Was this a speculative wren nest, for a second brood? I will have to step up the inspections and see what comes. While my hopes are dashed for bluebirds in '11, perhaps something just as interesting will come along. More news as I learn it...